PCB connections

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Note

The signals TDI, TMS, TCK, RTCK and TDO are
typically pulled up on the target board to keep them stable when
the debug equipment is not connected.

DBGRQ and DBGACK are typically pulled down on
the target.

If there is no RTCK signal
provided on the processor, it can either be pulled to a fixed logic
level or connected to the TCK signal
to provide a direct loop-back.

All pull-up and pull-down resistors must be in the
range 1K-100KΩ.

The VTREF signal is typically connected directly
to the VDD rail. If you use a series resistor to protect against
short-circuits, it must have a value no greater than 100Ω.

To improve signal integrity, it is good practice
to provide an impedance matching resistor on the TDO and RTCK outputs of the processor. The
value of these resistors, added to the impedance of the driver must
be approximately equal to 50Ω.